The production of normal paraffins provides the ability of upgrading products from straight runs of hydrocarbon streams derived from crude oil fractionation. In particular, straight run kerosene is further processed to separate out normal paraffins for higher valued products, such as used in the production of linear alkyl benzenes (LAB). Normal paraffins in the range of C10 to C13 are important precursors to LAB production, which is in turn used to produce linear alkyl benzene sulfonate (LAS). LAS is the predominant surfactant used in the production of detergents.
The large utility of detergents and other cleaners has led to extensive development in the areas of detergent production and formulation. While detergents can be formulated from a wide variety of different compounds much of the world's supply is formulated from chemicals derived from alkylbenzenes. The compounds are produced in petrochemical complexes in which an aromatic hydrocarbon, typically benzene, is alkylated with an olefin of the desired structure and carbon number for the side chain. Typically the olefin is actually a mixture of different olefins forming a homologous series having a range of three to five carbon numbers. The olefin(s) can be derived from several alternative sources. For instance, they can be derived from the oligomerization of propylene or butenes or from the polymerization of ethylene. Economics has led to the production of olefins by the dehydrogenation of the corresponding paraffin being the preferred route to produce the olefin.
The choice of carbon numbers is set by the boiling point range of straight run cuts from crude distillation. Kerosene boiling range fractions from crude oil provide heavier paraffins. Paraffins having 8 to 15 carbons are present in significant concentrations in relatively low cost kerosene. These paraffins have been a predominant source for linear alkanes and the leading source of olefin precursors for use in making LABs. Recovery of the desired normal paraffins from kerosene is performed by adsorption separation, which is one process in overall production of LABs. The paraffins are then passed through a catalytic dehydrogenation zone wherein some of the paraffins are converted to olefins. The resultant mixture of paraffins and olefins is then passed into an alkylation zone in which the olefins are reacted with the aromatic substrate. This overall flow is shown in U.S. Pat. No. 5,276,231, which is incorporated by reference in its entirety, directed to an improvement related to the adsorptive separation of byproduct aromatic hydrocarbons from the dehydrogenation zone effluent. PCT International Publication WO 99/07656 indicates that paraffins used in this overall process may be recovered through the use of two adsorptive separation zones in series, with one zone producing normal paraffins and another producing mono-methyl paraffins.
Adsorptive separation on a large scale does not allow for the moving of the adsorption bed, therefore the technology uses simulated moving bed technology. The simulation of a moving adsorbent bed is described in U.S. Pat. No. 2,985,589 (Broughton et al.), which is incorporated by reference in its entirety. The success of a particular adsorptive separation is determined by many factors. Predominant among these are the composition of the adsorbent (stationary phase) and desorbent (mobile phase) employed in the process. The remaining factors are basically related to process conditions, which are very important to successful commercial operation.
While adsorption separation technology allows for the separation of normal paraffins from a hydrocarbon mixture, there are problems in recovering higher molecular weight paraffins after the separation that currently limit the ability to recover higher molecular weight normal paraffins.